In recent years, among automatic transmissions mounted in vehicles and so on, an automatic transmission is proposed that performs so-called neutral control in which a clutch (such as a clutch C-1) transmitting power of an automatic speed change mechanism is released so as to be placed in a state immediately before slipping, for example, when a vehicle is determined to be stopped in a D (drive) range, thereby reducing a drag loss in a torque converter, and thus relieving a load on an engine in an idle state (refer to Patent Document 1). In a majority of the automatic transmissions that perform the neutral control, when an operation intended for starting the vehicle, such as turning OFF of a foot brake or turning ON of an accelerator, is detected, the clutch of the automatic speed change mechanism is engaged, thereby starting the vehicle with a good response.